The ensueing specification deals with improvement over U.S. Pat. Nos. 3,596,020 and 3,937,909 said patents being held by the current inventor. In the earlier patent, the switching mechanism can be seen to be substantially different structurally from that which is now under consideration, whereas the latter patent, while more closely similar to the instant application, provides structural dissimilarities to such an extent that the current disclosure constitutes an improvement thereover and will be made manifest when considered with the ensuing specification and claims.